The role of the fatty acid (FA) composition of triglycerides (TAGs) on sterol/sterol ester oleogels has been studied. Minor oil components of three vegetable oils with varying degrees of unsaturation (iodine values, IV) were removed. Typical oil quality parameters were determined before and after the treatment, and oleogels were produced using all six oils. Characteristic gel properties such as transition temperatures, mechanical properties and microstructure were tested. The results were compared regarding the impact of IV and the stripping procedure. Minor components were essentially removed during stripping, resulting in significantly different oil properties such as peroxide value, free FA and viscosity. However, peroxides formed rapidly in stripped flaxseed oil. Gel–sol transition temperatures and enthalpies were higher in gels from untreated oils and decreased with IV in samples with stripped oils. In contrast, the sol–gel transition was suppressed due to minor oil components in untreated oils. The effect of IV on gel formation was much less and linked to a lower solvent viscosity in more unsaturated oils. Nevertheless, gel firmness was significantly higher in oleogels from untreated oils and decreased slightly with IV in stripped oils. That was associated with differences in the arrangement of network building blocks, which was confirmed using atomic force microscopy. This study showed that the FA composition of TAGs has a limited effect on oleogel properties compared to those of minor oil components. The next part of this study focuses on modifying oleogel properties by adding selected minor components to stripped oils at varying concentrations.

The role of selected minor oil components on sterol/sterol ester oleogels was studied. Therefore, oleic acid, tocopheryl acetate and monoglycerides were admixed with three vegetable oils, having different fatty acid compositions. Before that, minor natural components were removed from untreated oils (purification). Moreover, purified oils were subjected to a humidity treatment to increase their water content. All additives retarded the molecular self‐assembly of sitosterol with oryzanol, and the effect was dose‐dependent. Gel hardness only increased at low concentrations of tocopheryl acetate and decreased in all gels at higher concentrations. In contrast, Gmax′ was invariable in samples with oleic acid and monoglycerides and increased in gels containing tocopheryl acetate and water. Therefore, Gmax′ does not necessarily relate to the gels' compression firmness. Atomic force microscopy showed that the microstructure of oleogels was considerably modified by the additives. In general, a packed surface of twisted, thick bundles of tubules may be associated with a stiffer gel. Moreover, a composite structure in gels with monoglycerides was visible and confirmed by differential scanning calorimetry (DSC). DSC was used to determine gel–sol transition temperature and was associated with the number of tubules in the gel. The gel–sol temperature increased in samples 1.0% w/w oleic acid and tocopheryl acetate and decreased in gels with monoglycerides and water. The results show that oleogel properties can be significantly modified by minor components with functional groups. That was associated with interactions with the sterol and sterol ester in solution and with the surface of the tubules (ferulic acid moieties of oryzanol) in oleogels.

The first part of this study showed that the triglyceride composition of purified oils has little impact on sterol/sterol ester oleogels. Hence, changes in the gels’ properties observed in previous studies must arise from minor polar components, particularly by changing the interactions within the fibrillar network. Selected molecules (oleic acid, tocopheryl acetate, monoglycerides, and water) were added to three purified oils to unravel the individual contributions introduced by different functional groups. While all additives retarded the molecular self-assembly of sitosterol with oryzanol, distinct effects were found for gel hardness, transition temperatures and enthalpies, strain sweep responses, and microstructure. It was discovered that the maximum storage modulus in the linear viscoelastic region does not necessarily relate to the gels’ compression firmness. In samples comprising oleic acid and tocopheryl acetate, discrete interaction mechanisms with the scaffolding elements were suggested since results between the two additives developed differently and were dose-dependent. A network supporting effect was suggested at low concentrations, in line with previous results for oils comprising low levels of thermal deterioration products. The microstructure of oleogels was considerably modified with additives. Unfortunately, effects are difficult to quantify due to the packed surface observed in AFM micrographs.

The role of solvent composition, in particular, minor oil components on sterol/sterol ester oleogels, has been studied recently [1]. Reportedly, deterioration products hamper network formation and modify the gel’s macroscopic properties, probably due to alterations of the scaffolding elements’ interactions. However, the role of the FA composition of TAGs has not yet been addressed. In this study, minor oil components of three vegetable oils with varying degrees of unsaturation (iodine values) were removed, and the oils were chemically and physically characterized before and after the treatment. Consequently, β sitostero/γ-oryzanol oleogels were produced, and the gel-sol (DSC) and sol-gel (rheology) transitions were monitored. Moreover, large and small deformation tests were performed, and the results were linked to oil parameters. In contrast to minor oil components, the FA composition has little impact on oleogel properties. The decline in gel hardness with IV is possibly linked to a lower solvent viscosity. However, a considerable drop in gel-sol transition temperature was observed with increasing IV indicating fewer elements of scaffolding. That was linked to the rapid formation of primary oxidation products in purified flaxseed oil during oleogel preparation, impairing tube formation. Similar to previous results on deterioration products, these minor components seem to aid network strength at low concentrations resulting in similar transition enthalpies and G’. That might be due to shifted network interactions in the presence of molecular species with functional groups. In the second part of this study, these modified interactions in the presence of selected minor components will be discussed.